lucy24 - 9:16 pm on Nov 1, 2013 (gmt 0)
I've never seen that particular string
I also didn't recognize any of the IPs. Cursory lookup turns up assorted apparently human ranges: I get two Sprint/Embarq, one Verizon Online and a (maybe) Hawaiian Telcom. ymmv. Compromised machines?
A flat block on the UA string can't do any harm.
Now, technically you don't need to do anything at all: they're asking for a nonexistent page, so the most they'll ever get is a 404. A 403 might save a teeny tiny bit of server resources (because it never has to go look for the file). But in this case it's more about emotional satisfaction.